1. Field of the Invention
The present invention relates generally to medical instrumentation, and more particularly to instrumentation for arthritis diagnosis. Specifically, the present invention relates to a device for the recording and analysis of sound emitted by the movement of human joints such as the knee.
2. Description of the Background Art
For at least 100 years, the crackling and grating sounds emitted by movement of arthritic knees have been considered during diagnosis. It was recognized that the motion of a diseased joint produces distinct sound waves or vibrations. But difficulties were encountered in distinguishing articular sounds from extrinsic sounds, such as noise due to snapping tendons, hand tremor, skin friction and other background noise.
It has only been in the last 10 years or so that instrumentation and methodology have been developed which may permit articular sound to be used as a reliable tool in the non-invasive identification of knee joint diseases. The instrumentation and methodology have been used primarily for research purposes, and are based upon the use of a noise cancelling microphone to pick up articular sounds relatively free from extrinsic sounds, and digital processing of the acoustic signal for recording, display and statistical analysis. The results of some of these research efforts have appeared in the medical literature.
Chu et al., "Detection of Knee Joint Diseases Using Acoustical Pattern Recognition Technique," J. Biomechanics, Vol. 9, pp. 111-114, 1976, discloses recording knee joint sound on magnetic tape during active movement of the knee. Background noise is minimized using the principle of "noise cancellation" thereby permitting analysis of what might be renamed an "acoustic signature." The signature is said to be the product of pattern recognition techniques applied to random noise. Studies of knee recordings covering normal, rheumatoid arthritic and degenerative knees are said to show that their respective waveforms, spectral patterns and statistical property of auto-correlation appear to be unique, and therefore, may well prove to be a promising non-invasive diagnostic tool for early detection of the type and extent of knee joint damage. A goniometer sensing the angle of the patient's knee joint was used to provide the horizontal sweep to an oscilloscope which displayed the acoustic signal; the waveform was captured by a polaroid camera. It was said that for the polaroid test, acoustical characteristics of waveform such as amplitudes, pulses and shapes are observed for the three different types of knee joint conditions, namely, normal, rheumatoid and degenerative cases.
Russell, "Clinical Utility of Acoustic Arthrography and Tendonography," Abstract, American Rheumatism Association, Annual Scientific Meeting, Anaheim, June 4-8, 1985, discloses that sounds produced by normal or rheumatic arthritic joints were recorded, stored in digital form, computer edited and printed graphically. Simultaneous video recording of joint motion allowed synchronization of mechanical and acoustic events. Flexion of rheumatoid knees exhibited higher (300 vs. 150 Hertz) peak sound frequencies with approximately twice the sound intensity as normal knees. The construction of a musculoskeletal acoustic data base is proposed.
"Noninvasive Test Can Distinguish Arthritic Joint by Noisy Movements," Internal Medicine News, Vol. 19, No. 11., p. 55, 1986 (citing Bol. Assoc. Med. P.R., 78:9-11, 1986), describes a rectifying-demodulating phonopneumograph developed by Dr. Casanova in which an acoustic signal from a transducer sensing joint crepitation is amplified, rectified, demodulated, and stored for visual analysis in an oscilloscope or with a chart recorder. Smooth contours were said to be frequently observed in patients with normal knee joints; curves characterized by multiple peaks occurred sometimes in normal and more often in arthritic joints. Sharp, brisk peaks were rarely seen in arthritic joints, and multiple peaks per wave were seen in both normal and arthritic joints on flexion or extension, but this pattern was more common in arthritic joints. Dr. Casanova's work is further reported in "Detecting Arthritis," U.S. News and World Report, p. 55, Aug. 18, 1986, which says that in a test with 19 people, a technique of amplifying sound vibrations made by joints in motion was 100 percent accurate in diagnosing eight patients with arthritis and eleven with normal joints.
While the above-described research efforts indicate that articular sounds can be used for diagnosing arthritis, the prior art instrumentation and methodology have not been applicable for routine diagnosis by the practicing physician due to the high cost of the instrumentation and the high degree of skill and judgment that has to be exercised by the physician in carrying out the methodology. In addition, the prior art instrumentation and methodology have not accurately simulated the conditions under which the human knee or other joint is subjected during normal daily life. The research efforts, however, evidence a long-felt need for an alternative to the exploratory arthroscopic surgery that has been the primary diagnostic technique employed by the practicing physician.